In conventional mass spectrometer systems, it is challenging to achieve high mass resolution of a precursor ion for MS/MS. While electrostatic traps have been used to achieve high mass resolution, this is done at the expense of first exciting ions within the trap and then ejecting ions that are not of interest, until only ions of interest remain. The remaining ions of interest can be subsequently ejected from the electrostatic trap, fragmented and analyzed. If it is desired to analyze other ions, the electrostatic trap must be refilled and other ions of interested selected in a similar manner. While these techniques can achieve high mass resolution, they are generally very wasteful of sample, which can often be available in limited quantities.